Respuesta :

Answer:

d = 3

Step-by-step explanation:

The common difference d between consecutive terms is

d = - 18 - (- 21) = - 18 + 21 = 3

d = - 15 - (- 18) = - 15 + 18 = 3

d = - 12 - (- 15) = - 12 + 15 = 3

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